The usual method of accelerating a projectile to high velocities in a short distance is by means of a cannon. In this method, a charge of gunpowder is detonated behind a projectile in the cannon's breech and is instantly transformed into high pressure gas. This high pressure gas exerts a propulsive force on the end of the projectile thereby accelerating it through the barrel to high velocity. Unfortunately, the acceleration force decreases very rapidly as the projectile moves through the barrel. The maximum muzzle velocities are about 1 or 2 km/sec. Therefore, the maximum effective range of a conventional cannon is about 30 km.
Another method for accelerating a projectile is by means of an "electromagnetic launcher". In this method, electrical energy is transformed into magnetic energy which propels the projectile via magnetic forces. The advantage of this method is that the high initial force can be sustained all along the accelerator. This enables an electromagnetic accelerator to launch projectiles at velocities significantly higher than that achievable with conventional cannons. In fact, a long electromagnetic accelerator will be able to launch a projectile at orbital velocities. Thus, in theory, an electromagnetic launcher offers the possibility of unlimited range.
Unfortunately, electromagnetic accelerators designed for launching projectiles at hypervelocities must be evacuated in order to eliminate the disturbing effects of atmospheric drag. Of course, when operating in the vacuum of space, this is not a problem. But it is a very annoying practical problem when contemplating the design of Earth-based, rapid-fire, electromagnetic cannons for battlefield operations. In order for the accelerating tube to be evacuated, it must be sealed off from the outside atmosphere. In the prior art, this is accomplished by mounting a thin diaphragm over the muzzle of the tube and pumping out the air. The projectile is introduced into the launch tube by means of an air-lock and launched by breaking through the diaphragm. But every time a projectile breaks through a diaphragm, the vacuum inside the launch tube is destroyed. Thus, in order to launch a new projectile, a new diaphragm has to be mounted over the muzzle and the tube has to be reevacuated. This becomes a very tedious and time consuming problem when contemplating rapid-fire operations. This problem becomes even more severe when the tube diameter is increased because the time required to reevacuate the tube after each launching increases due to the increased volume. Consequently, prior-art electromagnetic launchers have very small bores, just a few centimeters in diameter, and are not very long. Thus, in order to achieve hypervelocities, the projectiles must have very low mass that are on the order of a few grams. But when such low mass projectiles are fired into the atmosphere at high velocities, deceleration by atmospheric drag is substantial. This limits the effective range and greatly reduces accuracy. Thus, the theoretical velocity advantages offered by electromagnetic launchers appear to be more than offset by the negative affects of atmospheric drag. According to the prior art, they can only reach their full potential when operating in a vacuum environment.
Most of the current research in Earth-based electromagnetic accelerators is focused on the development of so-called "railguns" for impact fusion, or for small calibre hypervelocity kinetic energy weapons for close-in point defense. Unfortunately, the electric-to-kinetic operating efficiency of hypervelocity railguns are inherently low (usually below 25%). Furthermore, in these launchers the projectiles are accelerated by maintaining sliding contact with two parallel rails which cause severe surface deterioration. This deterioration is so severe, the rails usually have to be replaced or resurfaced after only a few launches.
There is another class of electromagnetic accelerators called "coaxial launchers". These launchers are basically linear synchronous motors and are well known in the prior art. There is no physical contact between the object being accelerated and the accelerating tube. In some designs, the electric-to-kinetic operating efficiency can exceed 99%. Coaxial electromagnetic accelerators suffer no deterioration and can be used an unlimited number of times without breakdown. Unfortunately, the efficiency and overall performance of coaxial launchers is not very high for small calibre bores. Consequently, since both railgun and coaxial launchers require evacuated accelerating tubes when projectiles are accelerated to hypervelocities, hypervelocity coaxial launchers have usually been designed for operation in a vacuum environment such as in orbit, or on the Moon's surface. This is because it becomes too impractical to pump out a large calibre, high volume accelerator after each launching.
In summation, prior art hypervelocity electromagnetic launchers designed for operation within the Earth's atmosphere have inherently low electric-to-kinetic operating efficiency, small calibre bores, short range, poor accuracy, and very low repetition rates. These characteristics are clearly unsuitable for large calibre munitions and the practical demands of high accuracy, rapid-fire battlefield operations.
What is needed is an effective method for loading a projectile into an evacuated, large diameter, launch tube without going through the time consuming process of operating an air-lock, and a method for maintaining or rapidly reestablishing a hard vacuum inside the launch tube after a projectile is fired through it. The aim of this disclosure is to provide practical solutions to these problems and, in particular, to develop these solutions to provide a rapid-fire electromagnetic accelerator capable of launching large bore, guided projectiles with unlimited range and pin-point accuracy to destroy any target on Earth, or in orbit above it.